Preprints
https://doi.org/10.5194/bg-2022-90
https://doi.org/10.5194/bg-2022-90
 
28 Apr 2022
28 Apr 2022
Status: this preprint is currently under review for the journal BG.

Temperature sensitivity of dark CO2 fixation in temperate forest soils

Rachael Akinyede1,2, Martin Taubert1, Marion Schrumpf2, Susan Trumbore2, and Kirsten Küsel1,3 Rachael Akinyede et al.
  • 1Aquatic Geomicrobiology, Institute of Biodiversity, Friedrich Schiller University Jena, Dornburger Str. 159, 07743 Jena, Germany
  • 2Department for Biogeochemical Processes, Max Planck Institute for Biogeochemistry, Hans-Knöll Str. 10, 07745 Jena, Germany
  • 3German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig, Puschstraße 4, 04103 Leipzig, Germany

Abstract. Globally, soil temperature to 1 m depth is predicted to be up to 4 °C warmer by the end of this century, with pronounced effects expected in temperate forest regions. Increased soil temperatures will potentially increase the release of CO2 from temperate forest soils, resulting in important positive feedback on climate change. Dark CO2 fixation by microbes can recycle some of the released soil CO2, and CO2 fixation rates are reported to increase under higher temperatures. However, research on the influence of temperature on dark CO2 fixation rates, particularly in comparison to the temperature sensitivity of respiration in soils of temperate forest regions is missing. To determine the temperature sensitivity (Q10) of dark CO2 fixation and respiration rates, we investigated soil profiles to 1 m depth from beech (deciduous) and spruce (coniferous) forest plots of the Hummelshain forest, Germany. We used 13C-CO2 labelling and incubations of soils at 4 and 14 °C to determine CO2 fixation and net soil respiration rates and derived the Q10 values for both processes with depth. The average Q10 for dark CO2 fixation rates normalized to soil dry weight was 2.07 for beech and spruce profiles, and this was lower than the measured average Q10 of net soil respiration rates with ~2.98. Assuming these Q10 values, we extrapolated that net soil respiration might increase 1.16 times more than CO2 fixation under a projected 4 °C warming. In the beech soil, a proportionally larger fraction of the label CO2 was fixed into soil organic carbon than into microbial biomass compared to the spruce soil. This suggests primarily higher turnover (i.e. growth and death) of microbial cells, and we speculate that this is related to lower clay content in the beech soil. Despite a similar abundance of the total bacterial community in the beech and spruce soils, the beech soil also had a lower abundance of autotrophs, implying a higher proportion of heterotrophs when compared to the spruce soil, hence might partly explain the higher biomass turnover. Furthermore, higher temperatures in general lead to higher microbial biomass turnover in both soils. Our findings suggest that in temperate forest soils, CO2 fixation might be less responsive to future warming than net soil respiration and that variations in site-specific parameters might affect microbial biomass turnover and resultantly, dark CO2 fixation rates and its temperature sensitivity in temperate forest soils.

Rachael Akinyede et al.

Status: open (until 09 Jun 2022)

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Rachael Akinyede et al.

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Temperature sensitivity of dark CO2 fixation in temperate forest soils Akinyede, Rachael, Taubert, Martin, Schrumpf, Marion, Trumbore, Susan, Küsel, Kirsten https://doi.org/10.17617/3.EFHWIY

Rachael Akinyede et al.

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Short summary
Soils will likely get warmer in the future and this can increase the release of carbon dioxide (CO2) into the atmosphere. As microbes can take up soil CO2 and prevent further escape into the atmosphere, this study compares the rate of uptake and release of CO2 at two different temperatures. With warming, the rate of CO2 uptake increases less than the rate of release, indicating that the capacity to modulate soil CO2 release into the atmosphere will decrease under future warming.
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